The present invention relates to the installation of fasteners in structures, and, in particular, to the safe and controlled installation of interference-fit fasteners through holes in structures.
The fasteners that hold structures together, particularly those structures that are subject to significant dynamic forces and/or pressure over their lifetime, such as aircraft bodies, bridges, vehicle bodies, buildings, ships, train bodies, material handling and storage equipment, ladders, scaffolding, and others, must be properly secured in order to ensure that the structure will perform as intended over its lifetime. For example, fasteners are used to hold together various segments of the structure, such as layers of the structure or overlapping portions of the structure, and/or to attach any type of component to the structure.
In many applications, interference-fit fasteners are used to properly secure the parts of a structure, especially those structures that require particularly reliable and strong connections. One example of an interference-fit fastener is a HI-LOK™ fastener, commercially available from Hi-Shear Corporation of Torrance, Calif. Interference-fit fasteners are fasteners that are slightly larger than the hole into which they are inserted. Thus, when the fastener is installed in a hole that is slightly smaller than the fastener, the structure tightly holds the fastener and a secure connection between the fastener and the structure is created. Connections or joints utilizing properly installed interference-fit fasteners are also less likely to suffer from fatigue failure because the interference between the fastener and the structure results in a compressive preload in the structure. The interference between the fastener and structure also reduces the likelihood that debris, moisture, or any other element will enter into the fastener/structure interface, which can affect the integrity of the connection. In addition, interference fit fasteners do not tend to rotate or move when a nut or other fastener-holding component is attached to an end of an installed fastener. All of these properties and characteristics of interference-fit fasteners and connections make them advantageous as compared to other types of fasteners and connections.
In order to install interference-fit fasteners, several hundred pounds of force are generally required to push the fastener into the hole in the structure. Thus, an installer must utilize some type of tool to apply the necessary force to the fastener and push it into the hole in the structure. In the past, installers have generated the force in a variety of manners, such as by using prybars, rivet guns, slide hammers, or C-clamps. Most, if not all, of these techniques require considerable skill and care on the part of the installer to avoid damaging the adjacent/surrounding structure. In addition, these installation techniques are often unsafe and pose ergonomic hazards to the installer. For example, when using a prybar for leverage to apply force to a fastener, the prybar can easily slip because there is no way to secure the prybar to the structure. When the prybar slips, it can cause significant physical harm to the installer and/or damage to the structure. In addition, when using a rivet gun to apply force to the fastener, the rod of the rivet gun must be aligned precisely with the fastener and held steady by the installer as the rod makes contact with the fastener to force the fastener in the hole. Ensuring that the rod directly contacts the fastener is a very difficult task because there is no way to ensure that once the rod of the rivet gun is aligned with the fastener it will stay in that position during rivet gun operation because the installer holding the rivet gun may inadvertently move. Thus, the rod of the rivet gun may make contact with only part of the fastener or not at all, which may damage the fastener and/or the structure. Once the fastener and/or the structure are damaged, they must be repaired or replaced, which increases the time, labor and expense of the installation process.
Thus, there is a need to safely, reliably, and effectively install fasteners in structures, particularly interference-fit fasteners that require several hundred pounds of force be applied to the fastener in order to insert it into holes in the structures. The needed fastener installation technique should be easy to align, maintain alignment, and carry out, such that installers do not have to have specific skills in order to install fasteners in structures. In addition, the fastener installations should be faster than previous manners of fastener installation.